Electric arc furnaces have been used for a long time and to an increasing extent for the production of steel by melting scrap iron or any other ferrous raw material, for example a pre-reduced ore.
Generally, an electric arc furnace comprises a melting vessel which is closed, in its upper region, by a dome-shaped detachable cover and is connected to one or more electrodes which are linked to a current source.
The melting pot comprises a bottom, in the form of a basin, which is lined with refractory material, and a cooled substantially cylindrical lateral wall, the bottom part of which is connected to the upper edge of the basin.
Each electrode is attached to the end of an arm which extends, in an overhanging manner, above the vessel and penetrates into the vessel vertically, passing through an opening in the cover provided for that purpose.
In order to carry out a casting operation, the furnace is opened by moving aside the cover and the electrodes, generally by rotation about a vertical axis. The raw scrap iron is charged into the furnace by means of conveying skips or "baskets" which are taken hold of and transported above the furnace by a charging crane which travels above the entire installation, each basket being provided with a drop bottom for the discharge of the scrap iron into the furnace.
Thus, a certain quantity of scrap iron, referred to as "the charge", is introduced into the vessel by means of one or more baskets.
The furnace is then again closed and the electrodes are lowered into the furnace. Electric current is applied and the electric arcs formed between the electrodes and the scrap iron bring about the melting of the scrap ion.
The molten metal is collected in the basin and forms a bath covered by a layer of dross. The furnace is generally mounted to tip on rounded-off supports, and the metal is cast by pouring or passage through a pour hole provided in the bottom of the basin and closed by a stopper rod or an external nozzle.
All these operations bring about considerable wear of the hearth of refractory material lining the basin, the state of which is examined after each casting operation, the refractor lining being repaired or replaced periodically.
The scrap iron may be charged cold into the furnace, but this causes an excessive consumption of electrical energy in bringing the charge from the ambient temperature to the melting temperature.
For this reason, it is generally preferred to use a less costly source of energy to heat the scrap iron before it is charges into the furnace.
In particular, since the melting of the scrap iron produces within the furnace, a considerable volume of very hot fumes attempts are generally made to recover the calorific power of the fumes to heat the scrap iron prior to its introduction into the furnace.